In recent years, flat panel displays are used in various commodity products and fields, and thus flat panel displays are required to have a large size, high image quality and low power consumption.
Under the circumstances, organic EL display devices, which include an organic EL (electroluminescent) element that utilizes electro luminescence of an organic material, are attracting great attention as all-solid state flat panel displays that are excellent as having capability of low voltage operation, quick responsivity and light emission.
Active matrix type organic EL display devices, for example, are provided with a thin film-like organic EL element on a substrate having a TFT (thin film transistor). In the organic EL element, organic EL layers including a fluorescent layer are laminated between a pair of electrodes. The TFT is connected to one of the pair of electrodes. Then, voltage is applied across the pair of electrodes so as to cause the fluorescent layer to emit light, whereby an image is displayed.
In the above-described organic EL display device, the organic EL element may deteriorate due to external moisture. Therefore, in order to prevent deterioration caused by the moisture, in a conventional organic EL display device, it has been proposed to form a low-moisture-permeable sealing resin around the organic EL element and filling the interior with a desiccant (a getter) by DAM & FILL process.
However, in the conventional organic EL display device, at the pixels in the vicinity of the periphery, damage to the luminescence property caused by moisture proceeds or cracking occurs in the desiccant layer in the vicinity of the periphery before the desiccant layer reaches its total moisture absorption amount, which may cause damage to the pixels and degradation in the display quality.
Specifically, in this conventional organic EL display device, moisture that has passed through the sealing resin is absorbed by the desiccant layer. However, since the moisture is absorbed before diffusing sufficiently into the desiccant layer, partial moisture absorption proceeds preferentially in the vicinity of the periphery rather than in the internal region. As a result, a part in the vicinity of the periphery of the desiccant layer reaches formerly its saturation of moisture absorption, and thus entrance of moisture into the pixels in the vicinity of the periphery cannot be suppressed, which may result in damage to the luminescence property. Further, as a result of moisture absorption, the desiccant layer is cured and shrunk. However, since the cure shrinkage proceeds only partially in the vicinity of periphery, sometimes the desiccant layer is distorted and cracked. The cracks in the desiccant layer affect the optical properties of the organic EL display device. Moreover, when the layer composing the pixels of the organic EL display device is affected by the above-described cracks, it may do damage to the luminescence property of the pixel.
Therefore, as described in Patent document 1 below for example, it is proposed in a conventional organic EL display device to interlay a first resin layer between a desiccant layer and an organic EL element, and the first resin layer has a moisture permeation higher than a moisture permeation of a second resin layer (sealing resin). Further, it is also proposed in this conventional organic EL display device that a first moisture-proof layer having a moisture permeation lower than that of the first resin layer is interlaid between the first resin layer and the organic EL element, and that a second moisture-proof layer having a moisture permeation lower than that of the first resin layer is interlaid between the desiccant layer and the first resin layer. Namely, in this conventional organic EL display device, the first moisture-proof layer is provided on the organic EL element, and the first resin layer is provided in the inner face of the second resin layer, and the second moisture-proof layer and the desiccant layer are laminated in this order within this first resin layer, and this first resin layer is provided on the first moisture-proof layer.
In this conventional organic EL display device, moisture that enters from the exterior into the second resin layer is not partialized in the periphery of the second resin layer but it diffuses within the entire first resin layer. And thus, it has been regarded that partial moisture absorption in the desiccant layer is suppressed and the moisture can be absorbed uniformly in the entire desiccant layer. Further in this conventional organic EL display device, the moisture that entered the first resin layer can be directed to the desiccant layer side preferentially rather than the organic EL element side, and thus, it is regarded as possible to be absorbed preferentially by the desiccant layer. In addition, in this conventional organic EL display device, after moisture has entered the first resin layer, the second moisture-proof layer can suppress immediate absorption of the moisture by the desiccant layer, and the moisture that has entered the first resin layer can diffuse without partiality in the entire first resin layer. It is regarded as a result that the moisture is absorbed uniformly by the entire desiccant layer, thereby preventing a partial moisture absorption by the desiccant layer.